The present invention relates generally to large scale grain cookers, and more particularly to a method and apparatus for continuous controlled hydration grain cooking.
Rice is normally cooked in batches using what is known as a xe2x80x9cfull absorption method.xe2x80x9d This entails placing a measured volume of rice in a vessel, submerging it in precisely the amount of water that the rice will absorb, and heating the water to a full boil. A measured amount of rice that matches the water in the vessel is then added to the water and the combination of water and rice is brought to a boil while simultaneously being mixed gently. Once the water is boiling the heat is turned down or off and the rice is allowed to sit in the water at a temperature of between 190-210xc2x0 F. for approximately 20 minutes or until all of the water has been absorbed and the rice is fully hydrated and cooked.
This method is used for most types of rice, such as long-grained rice, medium- and short-grained xe2x80x98stickyxe2x80x99 rice, brown and basmati rice. Flavored rice is made by mixing flavorings such as turmeric or saffron into the water before the rice is added so that the rice will absorb the flavoring. Pilaf rice is also cooked in the same way by sauteeing onions, garlic and other herbs and spices, adding the water, bringing the water to a boil, and finally adding the rice to absorb the mixed ingredients.
A second method of cooking rice is termed the xe2x80x9cexcess waterxe2x80x9d method. In this method, the rice is added to a volume of water in excess of the amount the rice will absorb. At the end of the cooking process, when. the rice is fully cooked and hydrated, there will be some free water. The excess water method cannot be used in cooking Asian style xe2x80x98stickyxe2x80x99 rice because the excess water washes the starch from the surface of the kernels and leaves the rice less sticky. This method also cannot be used for cooking flavored rice or pilaf rice because the excess water dilutes the flavorings. Flavorings for rice are generally very expensive and it is desirable not to waste them by washing them away with the excess water.
The full absorption method of rice cooking is always used in batch cooking of rice. This method works reasonably well when the batch size is small (1-5 lbs. per batch). However, it does not work well when the batch size is several hundred pounds. This is because cooked rice on the surface of the batch has a lower water content than the rice on the bottom of the batch, rendering the batch of uneven quality. The unevenness occurs because as the rice kernels absorb water the kernels swell and the batch rises slightly out of the water pool. Once the top layer of rice has emerged from the water it cannot absorb additional water; at the same time rice kernels at lower levels in the batch with excess water around them continue to absorb additional water. When using this method, where the rice batch is 8-24 inches deep, the top layers have a much lower water content than the rice in the lower layers. In fact, rice at the bottom of the batch is over hydrated, soft and spongy; rice in the middle layers is generally hydrated properly, and rice near the top is under hydrated.
Continuous cooking of all cereal grain and cereal products, including rice, is much more efficient than cooking in batches. However, up to the present time true continuous cooking of rice could only be accomplished using the excess water method, and even then it was only used in cooking simple long grained white rice.
In Asia a semi-continuous full absorption cooking method is employed. The Asian medium- or short-grained types of rice are pre-soaked in water for one to two hours before cooking. Small pots are filled with a precise amount of water and pre-soaked rice, then conveyed through an oven to cook the rice in assembly line fashion. This system is very expensive and complicated to mechanize or to perform robotically for the following reasons: each pot must be filled with exactly the right amount of water and rice; the cover must be mechanically placed on the top of the cooking vessel; the pot is then conveyed through the oven; the cover is removed and the cooked rice tipped out; and the pot must then be washed and conveyed back to the beginning to receive another batch of rice and water. A machine to cook 2000 lbs. per hour of sticky rice presently costs in excess of $1,000,000 USD.
An additional disadvantage of this type of rice cooking system is that the rice is not stirred during the hydration time in the oven. As a result rice at the bottom of the pot has longer water contact time than rice at the top of the pot. Again, this results in uneven quality as the rice on the top layers have a lower water content than the rice kernels on the bottom layers. Accordingly, the result is much the same as that of the commercial batch cooking systems, with one difference: even the rice in the middle layers of the batch are generally not properly hydrated.
No other continuous full absorption method of cooking rice has been devised other than the assembly line pot method. Evidently no one has been able to conceive of a way to control the water and keep it in contact with each kernel until all rice kernels absorb the proper amount of water.
Generally: The present invention relates to a method of cooking cereal grains and products made of cereal grains in a batch cooker or continuously in a continuous cooker with controlled hydration. Also disclosed is an apparatus for the batch cooking of cereal grains and for the continuous cooking of cereal grains using the full absorption cooking method. Using the method and apparatus disclosed herein, a large bed of uncooked particulate cereal product is heated by direct steam injection without being in the presence of liquid water until the product is thoroughly heated to a temperature of approximately 190-200xc2x0 F. Hot water, approximately 200xc2x0 F. is then metered and periodically sprayed onto the top layers of the cereal at a rate slightly higher than the absorption rate of the food product, thereby allowing the water to percolate down through the cereal to the bottom layers at a rate matching the rate at which the product absorbs it during its vertical migration. The cereal in its fully heated condition begins to absorb the water that coats the surface of the cereal kernels. By periodically metering and spraying more water onto the cereal grain layers at a rate slightly above the rate at which the hydrating kernels absorb the water, the kernels throughout the volume of product will hydrate at an optimal rate.
In a continuous cooker this process is employed while the cereal is conveyed horizontally from an inlet end of the cooker toward the discharge or outlet end. At the discharge end of the cooker the cereal grains are fully hydrated and have absorbed all of the cook water sprayed onto the kernels during its transit through the cooking apparatus.
Although this invention applies to any cereal grain (such as rice, wheat, oats, corn, etc.) or any product made from cereal grain (such as pasta, oat meal, risotto, etc.) the instant application refers to rice for purposes of illustration and example only.
The full absorption batch or continuous rice cooking process and apparatus of the present invention will produce high quality rice at a fraction of the cost of existing batch or continuous assembly line pot cooking systems. It can cook Asian short grained xe2x80x98stickyxe2x80x99 rice, flavored rice and pilaf rice. The cooking process is controlled precisely to result in the same quality as batch cooked rice.
Summary of the Inventive Method: Each type of rice has a sequence of stages in the full absorption cooking process: First, either immediately preceding or as product is loaded into the cooking vessel, the rice kernels are washed for approximately four minutes to remove dust and surface starch. This is an optional but preferable stage; i.e., the rice need not be washed before cooking. The washing is accomplished by spraying water onto the rice at a high rate through at least one nozzle and while the rice is still at a relatively low temperature. The rice does not absorb water during this stage. After washing, the rice is exposed to steam in a heating stage for approximately three minutes. This brings the temperature of the rice up to substantially the temperature of the hot water that will be sprayed onto the rice throughout the cooking stages, thus equilibrating the rice. During this xe2x80x98heatingxe2x80x99 stage the kernels remain hard, relatively impermeable, and absorb. very little water. For the next approximately thirteen minutes (13 to 18 minutes into the cook) most of the water that will be absorbed in cooking is sucked into the kernels as the water is sprayed onto the rice through a plurality of hot water nozzles during a xe2x80x98steam and hydrationxe2x80x99 stage. Then, for the next approximately five to seven minutes (18-25 minutes into the cook) the water absorption of the rice dramatically slows down and the rice begins to swell in the final cooking stage, i.e., the final steaming stage, which is accomplished by the extremely steamy air maintained in the cooking vessel generally. but especially in the region proximate the discharge end of the cooker. This final stage gives each kernel a plump firm texture. After cooking, the rice is conveyed through a discharge outlet and into discharge bin.
The surface tension of a small amount of water coating each rice kernel will hold the water in place without runoff. If additional water is sprayed onto the rice, the surface tension of the water will be overcome and the excess water will gravitate to a lower level. In contrast to all existing art, both the continuous and batch cooking methods of the present invention involve spraying hot water onto the surface of the rice at a controlled, metered rate so that the surface tension of the water keeps the cook water in contact with each kernel as the rice absorbs the water. By controlling the rate at which the water is sprayed on or pulsing the water spray on and off, the water seeps down through the layers of rice from top to bottom at the same rate as the water is absorbed by the rice kernels at all levels and layers. Furthermore, in the continuous cooking method, the rice is periodically moved longitudinally through the cooking vessel while simultaneously being mixed to ensure extremely homogeneous exposure time to cook water.
Summary of the Inventive Apparatus for Continuous Cooking: The present invention may be embodied as a continuous grain cooking apparatus or a batch grain cooking apparatus. The continuous cooking apparatus comprises a substantially horizontal vessel in which the hydration and cooking process takes place. The vessel may have either a single trough or twin, side-by-side troughs. In a vessel with a single trough is a motorized screw conveyor with a single auger; in a vessel with twin trough the screw conveyor comprises parallel, side by side intermeshing augers. For long grained rice or cereals that do not stick together, a single auger system is adequate. For sticky rice or sticky cereal products, such as risotto or hominy grits, the product will stick to the rotating screw and will not convey properly. Accordingly, a double auger system is more suitable for continuous cooking of such products.
The auger flights on the double auger system are wound such that by rotating the augers in a counter rotating direction, up in the center, the rice is pushed to center of the cooker conveyor as the rice is conveyed from the inlet toward the outlet.( The mound of rice conveyed through the vessel is referred to herein as a rice bed or a bed of rice.) When the augers"" direction of rotation is reversed the rice is pushed outwardly toward the sides of the vessel and away from the center or interior. By changing the direction of rotation on a preprogrammed interval, the rice bed will be spread out and then pushed together in the center repeatedly as the bed is conveyed toward the discharge end. This movement and agitation exposes a high percentage of the rice kernels to the water spray from above and continuously stirs the rice to promote even hydration.
Down the length of the auger the 360 degree auger flights may be intermittently separated by sections of shaft without flights and on which mixing bars, or spokes, are welded and radially disposed. The action of the counter rotating augers, which rotate upwardly in the center, has the effect of keeping sticky rice from sticking to the auger flights while the bars mix the hydrating rice. The auger flights on the opposing auger clean the product from the flights on the adjacent auger. The spokes may also be equipped with paddles affixed to their distal end to assist in mixing and moving rice, as well as cleaning product from surfaces within the spoke""s range of movement.
Along the bottom of the twin auger trough is a row of direct steam injectors. These injectors are oriented to inject steam into the moving rice as it is conveyed along. The continuous gentle stirring of the rice by the counter rotating augers keeps the water spray and steam evenly mixed with the hydrating rice.
The rice is metered into the inlet of the cooker either manually or, preferably, by an electronic weigh belt feeder or gravimetric screw feeder. As the raw, dry rice is metered into the cooker it may be washed with a heavy water spray using either cold or hot water and the excess water then drained out through a screen in the bottom of the cooker tub. Alternatively, washing may be accomplished outside the cooker, drained, and then conveyed onto the feeder using any of a number of suitable conveying devices, preferably an elevator conveyor. The washing removes dust and surface starch that collects on the kernels during the milling process. Wash water representing approximately ten percent (10%) of the weight of the dry rice will be held around the dry rice kernels due to water surface tension. If hot water is used in the wash, the heat from the hot wash water (200xc2x0 F.) increases the temperature of the rice as it is being washed.
The control of the rice feeder is electronically networked with the control of the cook water metering system and the agitation system through a programmable logic controller (PLC). This control system may be programmed to spray extremely precise amounts of hot water at any point in the length of the cooking vessel, and during any stage of the agitation cycle, to keep each kernel surrounded with a preferred amount of water as it hydrates. The control assures that an excess of water will not be sprayed onto the rice bed. Using prior methods, an excess of water is often sprayed onto the bed of rice during the cooking process, and the water tends to collect near the bottom layers of the bed. Using the present inventive apparatus and method, if water is sprayed on at too high a rate in one area, the paddles on the slowly rotating auger flights redistribute the excess water to less hydrated rice kernels.
The water spray rate is governed by the feed rate of the rice being fed into the cooker. The ratio of water to rice and the percentage of water flow at each point in the length of the cooker are controlled by a PLC. These variables can be independently programmed for any product being cooked (cereal grain or product made with a cereal grain).
To get good water spray coverage on the fill surface of the layers of rice being conveyed, the water metering system cycles on and off under precise control by the PLC program, which coordinates the rice gravimetric or weigh belt feeder. the auger motor, and the water flow control valve. The water flow is controlled with a sufficient flow rate to provide adequate spray coverage and is turned off automatically at each spray nozzle location when the proper metered amount of water has been sprayed on to match the hydration of the entire bed of rice. The pulsing of the water on and off controls the distribution of water from the inlet end of the vessel to the discharge end.
Flavorings and spices can be mixed with the cook water and sprayed onto the hydrating rice. Even cooked diced onions, garlic or tomato can be metered into the rice since the intermeshing augers will gently mix in these ingredients. Because there is no excess water to carry the ingredients away or to compromise the even distribution of these ingredients, the resulting finished rice dish is homogeneous throughout the production cycle. Large particulate products such as bay leaves can be added to the rice on a continuous basis and they will be mixed in thoroughly and evenly.
It is important that the rice be kept at or near 210xc2x0 F. during the full length of the hydration cycle, and it is also important that the environment above the rice be maintained steamy and moist throughout the full length of the cooker. To ensure the maintenance of this environment, the cover is sealed with a water seal or gasket system and the direct steam diffusers are positioned the full length of the cooker. Steam that is not condensed by the hydrating rice is contained above the rice and is locked in by the water sealed cover. The only place steam can escape is through small openings at the inlet and outlet of the cooker. The cook water sprayed onto the hydrating rice is continuously preheated to 195-200xc2x0 F. as it passes through a water heater either mounted on the cooker or located separately.
Summary of the Inventive Apparatus for Batch Cooking: The controlled hydration method and apparatus may also be adapted for use in a batch cooking process wherein the food product is not conveyed or moved in the cooking vessel or relative to the hydration source. As embodied in a commercial batch rice cooker, the batch cooking apparatus of the present invention provides means for water to be sprayed onto stationary rice in a batch cooking vessel at the same time steam injectors are injecting steam in the region immediately underneath the rice batch. The steam rising up through the batch heats the rice while the water seeping down from the top layers provides the moisture for proper hydration. Gravity distributes the cook water evenly from top to bottom hydrating every rice kernel properly.
This controlled hydration method of full absorption cooking can be used for cooking grains and cereals other than rice, including wheat, barley, oats, pasta and other food products with a cereal composition.